[Macro-EMG: methodology and problems of determining normal values using the common extensor muscle of the fingers as an example].

The macro-EMG technique registers simultaneously two different potentials from one motor unit. One signal is a single fiber potential, the other an unselective compound recording (macro) of the action potentials of all the muscle fibers within this unit. So motor unit size can be quantified by its electrical activity. Measured data can only be judged upon if normal data are available. These we compiled for the extensor digitorum communis muscle in 83 healthy volunteers. As parameters of the macro-potential amplitude, area and duration were evaluated. It is shown, that amplitude and area are sufficient to characterise a potential. The potential itself is strongly influenced by age and muscle volume. Diagnostic evaluation of the macro-potential is only possible within the context of the results of the single fiber recording and the estimation of fiber density. We found within 105 normal persons a fiber density between 1.2 to 1.9 without a significant dependence on age. With our normal data it is now possible to derive diagnostic conclusions from macro-EMG data.